1. Field of the Invention
The present invention generally relates to a rotary actuator and a method for assembling a rotary actuator. More specifically, the present invention can relate to a hydraulic rotary actuator such as might be used in a motor vehicle suspension, and also to a method for assembling such a hydraulic rotary actuator. Such a rotary actuator in a motor vehicle suspension generally can be a part of a divided stabilizer on an axle of the vehicle. The actuator can essentially be formed by a cylinder, the ends of which would typically be closed to define e working space within the cylinder. The cylinder can have ribs which run axially on the inside diameter of the cylinder, and there can also be a motor shaft with vanes which have essentially the same axial extension as the ribs of the cylinder. The vanes of the motor shaft and the ribs of the cylinder divide the working space into individual work chambers. First and second hydraulic connections can be provided for two separate work chambers, and a connection system can be provided between the work chambers to form a hydraulic connection between at least pairs of work chambers, whereby the orientation of the connected work chambers is such that the work chambers corresponding to the first hydraulic connection alternate with the work chambers which are connected to the second hydraulic connection.
2. Background Information
A general problem with motor vehicles has been a rolling motion which occurs during cornering. Attempts to solve this problem have long employed a divided stabilizer which is connected, at its connecting surfaces, to a rotary actuator. By means of the rotary actuator, the torsion moment in or on the stabilizer can be controlled so that, for example, when the vehicle is travelling straight ahead, the stabilizer does not influence the suspension action at all, or only very little, but during fast cornering, the stabilizer provides a bias to suppress the rolling motion and thus the tendency of the vehicle to tilt to one side.
German Patent Application No. 1 179 124 discloses a rotary actuator for a divided stabilizer. In this rotary actuator, the end caps are bolted to a cylinder to form the working space. This solution, which employs threaded fasteners for a connection between the caps and the cylinder, is not only excessively expensive, but also takes up a great deal of space. There is an extremely small amount of space available inside a stabilizer for the installation of a rotary actuator. For stabilizers on the front axle, the stabilizer frequently runs into a space conflict with parts of the engine, for example, the oil pan, or possibly the radiator. Similar problems often occur on the rear axle as a result of the exhaust system, the trough for the trunk or the spare tire.
The outside diameter of the rotary actuator is not the only dimension which must be taken into consideration to solve the problem of installation space, as the axial length of the component is also important. In known actuators, a major portion of the length is taken up by the connection system between the work cheers of the working space. In Federal Republic of Germany Patent Application 1 179 124, the connection system consists of a series of discs that are located between the working space and one of the end caps. But after a certain surface area of the vanes or ribs inside the rotary actuator has been mathematically specified for a specified moment, the sequence of the connection system takes up an axial length which makes the rotary actuator longer without increasing its moment.
The rotary actuator disclosed in German Patent Application No. 1 175 563 seems at first glance to solve the problem described above. But, with this actuator, there is an additional problem, in that each work chamber has a separate hydraulic connection, i.e. ultimately there is no internal connection system. Each of the separate hydraulic connections represents a potential source of uncertainty with regard to leaks, as the hydraulic lines underneath the vehicle are exposed to the effects of heat, humidity and abrasive substances. In addition, because of the constant motion of the components of the stabilizer, the hydraulics connections can also be subjected to essentially constant movement, which might tend to loosen the connection Joints.
British Patent GB 657 873 discloses a rotary actuator, which comprises a cylinder which is closed on the end and forms a work space, ribs which run axially on the inside diameter of the cylinder, and a motor shaft with vanes which have the same axial length as the ribs of the cylinder. The vanes of the motor shaft and the ribs of the cylinder divide the work space into individual work chambers. In addition, the rotary actuator also has a first and a second hydraulic connection for two separate work cheers, and a connection system between the work chambers which hydraulically connects at least pairs of work chambers, whereby the connected work chambers are connected so that the work chambers corresponding to the first hydraulic connection alternate with those connected to the second hydraulic connection.
While the rotary actuator described herein is described in conjunction with use in a motor vehicle suspension, it should be noted that rotary actuators are used not only in vehicle suspension systems, but are also widely used in industry, whereby the same problems can typically occur as in the application described above.